1. Field of the Invention
The present invention relates generally to a liquid crystal display (LCD) and more specifically to a LCD which is provided with measures for shunting or discharging static electricity which may be generated during fabricating and/or repairing the LCD.
2. Description of the Related Art
As is known in the art, LCDs are commonly used in portable computers and other small, microcomputer-controlled devices for displaying data and graphics generated by these devices.
Before turning to the present invention it is deemed preferable to briefly describe, with reference to FIGS. 1 to 3, a conventional LCD which is disclosed in Japanese Laid-open Patent Application No. 4-153625.
FIG. 1 is a sectional view of a conventional active matrix type LCD which is generally denoted by numeral 10. FIG. 2 is a plan view of part of a TFT (thin film transistor) substrate on which various elements including TFTs are disposed, while FIG. 3 is a perspective view of a liquid crystal seal provided on another transparent substrate.
The LCD disclosed in the aforesaid Japanese Patent Application is directed to a liquid crystal seal which, in addition to confining a liquid crystal layer, is able to electrically interconnect two electrodes respectively provided on opposing two substrates. Other than this, the arrangement is well known in the art and thus, only a brief description thereof will be given for simplifying the disclosure.
As shown in FIG. 1, two transparent (e.g., glass) substrates 12 and 14 are provided in a manner wherein they oppose each other and are spaced apart by about 10 .mu.m (for example). Throughout the instant disclosure, the substrate 14 is referred to as a TFT substrate in that the main element disposed thereon is the TFTs. A liquid crystal layer 16 is confined in a space defined by the substrates 12 and 14 along with a liquid crystal seal 18. This seal 18 is provided at the periphery of each of the substrates 12 and 14 and is sandwiched therebetween. A pair of polarizers 20 and 22 are respectively attached to one of the major surfaces of each of the substrates 12 and 14 as shown in FIG. 1. The substrate 12 carries a color filter 24 on its inboard surface. The color filter 24 is substantially entirely covered by a common electrode 26 which is then coated with an alignment layer 28.
As best shown in FIG. 2, the TFT substrate 14 supports a plurality of bonding pads 30 and 32, an electrode 34, a plurality of pixel electrodes 36 arranged in matrix, a plurality of MOS (metal oxide semiconductor) TFTs 38 respectively coupled to the corresponding pixel electrodes 36, a plurality of column (e.g. drain) lines 40, and a plurality of row lines (e.g., gate) lines 42, and a lead 44 for electrical interconnection between the pad 32 and the electrode 34.
The liquid crystal seal 18 is formed, using a known screen printing technique, at the periphery of one major surface of the substrate 12 in the manner shown in FIG. 3. Thereafter, the substrate 12 is aligned and pressed on the TFT substrate 14 under a high temperature ranging from about 150.degree. C. to 230.degree. C., whereby the seal 18 is secured between the substrates 12 and 14. It is to be noted that the liquid crystal seal 18 is provided with an opening for injecting a liquid crystal material. This opening is closed or sealed when the liquid crystal layer 16 is established. The closed opening is indicated by numeral 45.
The liquid crystal seal 18 is generally comprised of epoxy resin and is functionally divided into a first portion (depicted by A) and a second portion (depicted by B) as indicated in FIG. 3.
That is, the first portion A is pressed on the electrode 34 (FIG. 2) and includes a plurality of electrically conductive spherical spacers 46 (FIG. 1) which are embedded in the epoxy resin. Each conductive spacer 46 is a plastic bead (for example) which is coated with silver, gold, etc., which is elastically deformable, and which has a diameter slightly larger than a space between the substrates 12 and 14, in which the spacer is disposed. Therefore, the spacers 46 are able to establish electrical connections between the electrode 34 and the common electrode 26. More specifically, the reason that the conductive spacers 46 are embedded for the purpose mentioned above is that the lower surface of the substrate 12 is not provided with any electrode for directly supplying electricity to the common electrode 26.
The second portion B of the seal 18 is disposed on the peripheral portion of the TFT substrate 14 in addition to the electrode 34, as indicated by dashed lines in FIG. 2. This second portion B includes a plurality of non-conductive spherical spacers 48 which are also embedded in the epoxy resin. Each of the non-conductive spacers 48 is a plastic bead (for example), which is elastically deformable, and has a diameter slightly larger than a space between the substrates 12 and 14, in which the spacer is provided.
Further, in order to secure a predetermined distance between the substrates 12 and 14, in the region of the liquid crystal layer 16, a plurality of spacers 50 are provided in the manner shown in FIG. 1.
When the LCD 10 is installed in a device, a backlight is applied from behind the polarizer 22 as shown in FIG. 1.
The above mentioned conventional LCD, however, does not give any attention to preventing damage by electrostatic discharge which may occur during fabricating the LCD and/or repairing the same.
More specifically, as is well known in the art, a plurality of TFT substrates 14 are fabricated on a large single glass plate at the same time. After the deposition of elements such as TFTs on the glass plate is finished, the glass plate is cut into individual substrates 14. When cutting the glass plate, static electricity may be developed and stored on the substrates 12 and 14. Further, the same discussion may hold while transporting and handling the TFT substrates. Still further, after an LCD equipped device is handed to a user, when the top polarizer 20 is damaged and to be replaced by a new one, undesirable static electricity may accumulate on the substrate 12 (and 14) during the repairing. All TFTs are extremely susceptible to gate oxide breakdown, caused by electrostatic discharge. Therefore, it is important to consider how to cope with the damage by electrostatic discharge.
In addition to the aforesald conventional LCD disclosed in Japanese Patent Application No. 4-153625, each of Japanese Utility-model application No.61-89819 and Japanese Laid-open patent application No. 62-218937 discloses a liquid crystal seal which includes a plurality of conductive spacers similar to the spacers 46. However, none of these provide any teaching or suggestion for preventing an LCD from being damaged by electrostatic discharge.